1. Field of the Invention
The present invention relates to a floating gate type nonvolatile semiconductor memory device and a write method of the same.
2. Description of the Related Art
In an n-type memory cell of the conventional NAND flash memory having a floating gate, data write, erase, and read are performed as follows.
In data write, a high positive voltage is applied to a control gate electrode to inject electric charge into a floating gate electrode from a channel below the floating gate electrode through a tunnel oxide film by FN tunneling. This increases the threshold voltage of a cell transistor. In data erase, a positive voltage is applied to a substrate to extract electrons from the floating gate electrode to the substrate by FN tunneling. This decreases the threshold voltage of the cell transistor. In data read, the data is discriminated by the amount of electric current when a voltage is applied to an arbitrary control gate electrode.
In the conventional charge storage flash memory as described above, a so-called Yupin effect in which the apparent threshold voltage changes due to the influence of electric charge in an adjacent floating gate electrode is unavoidable, and this Yupin effect deteriorates the operation characteristics of a cell. Also, the Yupin effect occurring in the conventional charge storage transistor becomes notable as the micropatterning of cells advances. This complicates circuit operations, and makes the micropatterning of cells difficult.
Note that prior art reference information related to the present invention is as follows.
[Non-patent Reference 1] K. Terabe, T. Hasegawa, T. Nakayama & M. Aono. Quantized conductance atomic switch. Nature 433, 47-50 (2005)